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The jungle in Thailand is home to groups of langurs, Phayre’s leaf monkeys, and the life team have come here to film their behaviour. The guide is Eileen Larney, a graduate student from StonyBrookUniversity who knows the monkeys well as she’s worked here for nine years.

Eileen Larney

In 2000 Dr Andreas Koenig and Carola Borries set up this site and we started with the Phayre’s leaf monkeys then and I came first as a field assistant with them and we didn’t even know what the langurs looked like and we slowly started to habituate them. Initially they were very afraid of people, they would, because they had been poached in this area for different Chinese medicinal medicine, so we slowly but surely started following specific groups that were slightly further from the road so that you wouldn’t have human influence, as they got used to humans at least they would be protected further into the forest. And we began following groups and it takes about a year to a year and a half to two years to get them habituated enough that we don’t provision them at all, we just like to watch them in their wild state.

The species we work with is Trachypithecus phayrei and they’re called Phayre’s leaf monkeys; sometimes we call them langurs as well. They are primarily leaf eating monkeys; they have a multi-chambered stomach to digest leaves, although they do spend a large proportion of the time eating fruits and seeds as well. In this population they live in one male as well as multi-male groups and average group size is around 20 or so individuals, and it ranges from a group of 12 to sometimes about 30 or maybe even more, and our species females disperse from their group.

So, in many other primate species the females stay in the group which they’re born but in this species we found females leaving their group when they reach about sexual maturity, which is about four to five years of age, and they’ll transfer to different groups and temporarily visit different groups until they settle on one or even reproduce in a group and then go to another one. And the males we’re still, you know, even after all this time we’re still not 100% sure what’s going on with them but we do have males that mature in their group that they’re born in and will then reproduce as long as their mother or sisters aren’t in that group, which they usually decide to leave if that is the case. But we do have some males disappear but right now we don’t have any individuals that we recognised any adult males having gone to a different group, but still time will tell what happens with those.

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For adult males that stay with the group there’s the risk of confrontation. Eileen has found a lone male quite near to the ground and is able to get a closer look.

Eileen Larney

So, yesterday morning there was a fight between this adult male and two of the adult males in the group, and they basically started barking in the morning which we have the vocalisations for and then one male fell which we have come to find out is this male, and he’s disappeared for two days and is now trying to get back into the group, but we’re waiting to see how the other males react to him coming back. Already there’s been some jumping displays and he’s just staying on the periphery of the group at the moment so we’ll see what happens from this point on. But he has a big gash on his right thigh and he also has some cuts on his chin and that looks like it for now. It doesn’t seem like anything is broken though, or anything, so at least that’s good.

The rangers we work with daily are wonderful. They are the constant presence here because we come and go as students but they’re here, they know the monkeys, they see them through years, are just as involved, if not more, in the project as we are and they are trained in all the behavioural methods then teach the new assistants that come. And you just want to keep things as wild as possible and have as limited an impact as possible, and here in Thailand it’s been really fortunate that we’re able to have this project running very smoothly.

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Originally published: Saturday, 28th November 2009

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